This invention relates to a magnetic recording medium. Particularly, it relates to a magnetic recording medium excellent in electric characteristics and reliability.
As magnetic disks with higher recording density are desired, there have been proposed magnetic disks of various structures. As to coating-type magnetic disks, there are known, as disclosed in Japanese Patent Application Kokai (Laid-open) Nos. 56-169,226 and 57-167,135, ones wherein the surface roughness of a particular track has been made larger than that of the recording track surface. As to sputtering disks, there are known, as disclosed in Japanese Patent Application Kokoku (Post-Exam. Publn.) No. 61-36290, one wherein the inner and the outer periphery of the magnetic disk have been made to have different coercive forces or, as disclosed in Japanese Patent Application Kokoku (Post-Exam. Publn.) No. 58-43818, one wherein the spaces between recording tracks have been made non-magnetic by ion implantation. Although it is possible in a sputtering disk to make the inner and the outer periphery of the disk have different coercive forces, it is not easy in a coating-type magnetic disk wherein the film is formed by spin coating. For a coating-type magnetic disk, the only attempt so far made is to form one kind of magnetic film on one substrate and process it such that a particular track will have a more rough surface than other parts. No consideration has ever been given to applying different, two or more kinds of coatings onto different regions on one substrate and thereby forming films having utterly different functions.
The prior art techniques mentioned above give, as can be seen in the example of coating-type magnetic disks, no consideration to forming films, having utterly different functions, on different regions of one substrate, and thereby obtaining a magnetic disk more excellent in electric characteristics and reliability. Thus, they have a problem in that a marked improvement of magnetic disk characteristics cannot be expected by such techniques.
The drawbacks of the conventional coating type magnetic recording medium such as mentioned above can be summarized as follows:
(i) In the case of a one-shot coating type magnetic recording medium, writing in the outer zone of the disk is usually difficult, compared with that of the inner zone thereof since the film in the outer zone is always made sufficiently thicker so as to meet the high speed of the magnetic head in said zone compared with that in the inner zone. PA1 (ii) For the purpose of protecting the surface of the disk, .alpha.-alumina having a particle size being larger than the thickness of the coating film at 20% is used. Since the coating film of the inner zone is thin while that of the outer zone is thick, it would be difficult to choose .alpha.-alumina having a suitable particle size as a hard filler in the case of one-shot coating. PA1 (iii) In order to reduce the abrasion coefficient of the surface of the disk, a liquid lubricant is usually used. However, this brings such a problem that the magnetic head adheres to the surface of the disk during a non-operation period in which said head contacts closedly onto the surface of the disk if a considerable amount of said lubricant is used in such a zone so as to enable smooth operation. Moreover, such adhesion may result in damage to both the magnetic head and disk.